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To best use valuable space, Greg Lang planted rows close and trained trees tall and narrow into a fruiting wall. Above is the solid-set canopy delivery spray system that replaces conventional tractor-pulled sprayers.

To best use valuable space, Greg Lang planted rows close and trained trees tall and narrow into a fruiting wall. Above is the solid-set canopy delivery spray system that replaces conventional tractor-pulled sprayers.

Dennis Hoxsie has both moral support and helpful advice from Dr. Greg Lang, the Michigan State University horticulturist who was bitten by the high tunnel bug six years ago and has been intensively researching them ever since.

What Hoxsie wants to do—have high quality sweet cherries earlier than those around him—has been one of Lang’s goals as well.

Lang began his research in 2005, when three multibay high tunnels 28 feet wide and 160 feet long were built over a portion of a high-density planting of six-year-old sweet cherries at Michigan’s Clarksville Horticultural Research Station. Also in 2005, four multibay tunnels 24 feet wide and 200 feet long were built at the Southwest Michigan Research and Extension Center near Benton Harbor, and cherries were planted in them.

The first year, Lang focused on the obvious use of tunnels for rain protection by only covering the bearing trees at Clarksville during ripening. However, he questioned the conventional wisdom that young trees should not be covered during the first three years to save on the cost, and extend the life of the plastic.

With the new orchard at Benton Harbor, Lang found it was more important to install the covers from the moment of planting to get fast growth and fill the space early. Covering the young trees from bud break through most of the growing season had a big impact. Trees were 24 ­percent taller, leaf size was 20 percent larger, and trunks were 35 percent bigger. He wants fruit in year three and full production by year five.

In 2008, Lang covered and enclosed the sides and ends of both orchards prior to bud break and had contrasting results: At Clarksville, the trees bloomed early, set fruit, and avoided a damaging frost that occurred when the outside trees were at full bloom. However, at Benton Harbor, he found that on clear sunny days, temperatures rose quickly to 115°F, “converting Benton Harbor in March to Bakersfield in July,” he said, which damaged the flower buds of those trees.

In 2009, he did what Hoxsie wants to do—covered each tunnel bay at different dates to see how it affected bloom date, ripening date, shoot growth, and fruit size. He put ­covers on in weekly intervals over four weeks starting March 17. While he managed the interior temperatures at bud break better than in 2008, it also required some effort to manage excessive heat, he said. A hot, humid spell in June near harvest lowered the quality of several varieties at susceptible stages of ripening.

The earliest-covered cherries bloomed April 17, 11 days ahead of those not covered at all. Each week of delay in covering delayed bloom four days.

The longest-covered Rainier cherries ripened on June 22 and Skeena on June 30—both seven to ten days earlier than in Washington. All fruit was harvested on June 22 and measured for size and sweetness. The Rainier cherries were 34 millimeters in diameter (about 8-row) in the earliest-covered trees, and were smaller in later covered, down to 25 mm without tunnels. Brix was 14.3 in the uncovered cherries and ranged up to 18.8 in the cherries covered the longest. Weight also varied, with those covered longest at 15.5 grams per cherry compared to seven grams for the uncovered cherries. A 10-row cherry weighs just under ten grams.

In the variety trials, Lang found 30 varieties averaged ten grams or larger in fruit size, with three Washington selections averaging 15 grams and one Cornell selection on G.5 weighing 16 grams.

New trials

Because high tunnel space is expensive, Lang wants higher density plantings with trees no taller than eight feet for easy harvest.

To achieve this, at Benton Harbor he planted an additional row of cherries down the tractor drive alley. He is pruning and training all the trees into fruiting walls and has installed a “solid-set canopy delivery spray system.” Instead of using a vehicle and sprayer, a system of polytube irrigation lines and emitters was fastened overhead onto the high tunnel metal frame and used to apply pesticides, plant growth regulators, and fertilizer. It is not used to irrigate. Drip lines on the ground provide irrigation water.

Lang is experimenting with the Upright Fruiting Offshoot (UFO) system developed at Washington State University, as well as a bilateral cordon system, a tall spindle axe system, and a super slender axe system.

The idea, he said, is to optimize the space for trees, not tractors. He now thinks a 26-foot-wide tunnel would be ideal, giving five feet of open space to the walls and eight feet between the three rows. A tree spacing of five- by eight-feet gives 1,012 trees per acre; making trees eight feet tall gives a fruiting volume of 1.25 cubic meters per square meter of tunnel space, a 25 percent increase over the previous lower density system.

To make best use of light, the entire floor is covered with reflective material to bounce light back into the tree. “Having plastic covers already reduces light intensity by about 25 percent,” he said, “about the same as one layer of leaves.”

Lang is still working to perfect it all: getting the best growing degree unit accumulation without risk of collapsing the tunnel under snow or getting frost damage by encouraging early breaking of dormancy; preventing excessive heat build-up; figuring out the best soil and water management; protecting the system from high winds; and getting an ideal plastic cover for the best light spectra and quantity.

“High tunnel cherries are kind of expensive,” Lang said. “But if you’re getting the kinds of returns we’ve seen—you’ve got the right market and the right cherries—you can start thinking about them, especially if you can get more from the investment than just rain protection.”

Hoxsie and a few other growers—in Michigan and across the Northeast and Midwestern United States— are taking the plunge, hoping Lang can solve the ­problems as they crop up.